Size and Shape of the Cerebral Cortex in Mammals

Abstract

The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain – irrespective of convolutedness or ecological strategy – as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as well.

The use of pigs in neuroscience: Modeling brain disorders

“…Anatomy of the porcine brain 3.1.1. Comparative neuroanatomy Whereas the rat cerebral cortex is lissencephalic, the pig brain cortical surface more closely resembles human gyrencephalic neocortex (Hofman, 1985). Similarities in the gross anatomy of pig brain to that of human brain has also been demonstrated for the hippocampus, a limbic structure (Dilberovic et al, 1986;Holm and Geneser, 1989), as well as for subcortical and diencephalic nuclei (Felix et al, 1999;, and brainstem structures (Freund, 1969;Ostergaard et al, 1992).…”

“…Descriptive on basis of size and shape Hofman (1985) Sulci and gyri patterns Descriptive on basis of size and shape Campbell (1905), Rawiel (1939), Stephan (1951), Kruska (1970) Geneser (1989, 1991a, b) Immunocytochemistry Holm et al (1990Holm et al ( , 1992Holm et al ( , 1993) Stereology Holm and West (1994) Basal ganglia Immunohistochemistry Matsas et al (1986) PET receptor binding Ishizu et al (2000), Rosa-Neto et al (2004a, b) Diencephalon…”

An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain

“…Where it was not given in the original reference, the cortical volume was calculated by multiplying the cortical surface area by 0.175, which is the maximum cortical thickness reported for Tursiops truncatus (range 1.3-1.75 mm ; Ridgway & Brownson, 1984). Data sources : (1) Hofman (1985Hofman ( , 1988 ; (2) Ridgway & Brownson (1984) ; (3) Kesarev et al (1977) ; (4) Stephan et al (1981) ; (5) Pirlot & Nelson (1978) ; (6) suggests that less of the cetacean cerebral cortex is devoted to computation, and more is occupied by wiring, which may impact negatively on the computational power of the cetacean brain.…”

Principles underlying mammalian neocortical scaling

“…By con®ning area counts to within a single methodology (i.e., that of Kaas and colleagues), we expect a reasonable estimate of the exponent. Brain volumes are taken from Frahm et al (1982), Haug (1987), Hofman (1982aHofman ( ,b, 1983Hofman ( , 1985, Hrdlicka (1907), and Stephan et al (1981). The x-axis is brain volume, but since it scales proportionally to gray matter volume (see caption of Table 1), the slope of the line in the plot gives the best-®t exponent for the number of areas as a function of gray matter volume.…”